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spapr: Ensure all LMBs are represented in ibm,dynamic-memory

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Memory hotplug can fail for some combinations of RAM and maxmem when
DDW is enabled in the presence of devices like nec-usb-xhci. DDW depends
on maximum addressable memory returned by guest and this value is currently
being calculated wrongly by the guest kernel routine memory_hotplug_max().
While there is an attempt to fix the guest kernel, this patch works
around the problem within QEMU itself.

memory_hotplug_max() routine in the guest kernel arrives at max
addressable memory by multiplying lmb-size with the lmb-count obtained
from ibm,dynamic-memory property. There are two assumptions here:

- All LMBs are part of ibm,dynamic memory: This is not true for PowerKVM
  where only hot-pluggable LMBs are present in this property.
- The memory area comprising of RAM and hotplug region is contiguous: This
  needn't be true always for PowerKVM as there can be gap between
  boot time RAM and hotplug region.

To work around this guest kernel bug, ensure that ibm,dynamic-memory
has information about all the LMBs (RMA, boot-time LMBs, future
hotpluggable LMBs, and dummy LMBs to cover the gap between RAM and
hotpluggable region).

RMA is represented separately by memory@0 node. Hence mark RMA LMBs
and also the LMBs for the gap b/n RAM and hotpluggable region as
reserved and as having no valid DRC so that these LMBs are not considered
by the guest.

Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
Bharata B Rao 2016-06-10 10:44:48 +05:30 • committed by David Gibson
parent bc9ca5958d
commit d0e5a8f293
2 changed files with 40 additions and 21 deletions
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6
include/hw/ppc/spapr.h
View file

@ -620,9 +620,11 @@ int spapr_rng_populate_dt(void *fdt);
#define SPAPR_DR_LMB_LIST_ENTRY_SIZE 6
/*
* This flag value defines the LMB as assigned in ibm,dynamic-memory
* property under ibm,dynamic-reconfiguration-memory node.
* Defines for flag value in ibm,dynamic-memory property under
* ibm,dynamic-reconfiguration-memory node.
*/
#define SPAPR_LMB_FLAGS_ASSIGNED 0x00000008
#define SPAPR_LMB_FLAGS_DRC_INVALID 0x00000020
#define SPAPR_LMB_FLAGS_RESERVED 0x00000080
#endif /* !defined (__HW_SPAPR_H__) */